The invention is directed to exploiting photon-assisted tunneling in high transition temperature superconductor structures for use as an infrared photon detector. One application is an infrared photon detector optimized for the detection of cold bodies in space, i.e., whose operating spectral response is in the wavelengths of about 10 .mu.m to about 100 .mu.m at a temperature of 77.degree. K. or higher.
The detection of cold bodies in space is a most difficult technical problem. The wavelengths of interest lie generally in the 10 .mu.m to 100 .mu.m spectral interval. A widely used prior art detector Hg.sub.1-x Cd.sub.x Te (i.e., Hg.sub..795 Cd.sub..205 Te) operating at 77.degree. K., is limited to wavelengths less than 12 .mu.m as has been shown by Kruse, "The Emergence of Mercury Cadmium Telluride as a Modern Infrared Sensitive Material:" Chapter 1 of Semiconductors and Semimetals 18, Mercury Cadmium Telluride, R. K. Willardson and A. C. Beer, eds. Academic Press, New York (1981). To achieve longer wavelength operation requires a smaller value of "x" in the Hg.sub.1-x Cd.sub.x Te, such as Hg.sub..82 Cd.sub..18 Te. A strong disadvantage however, is that the lower value of "x" requires cooling to temperatures below 77.degree. K. Another limitation of small bandgap Hg.sub.1-x Cd.sub.x Te, i.e. (Hg,Cd)Te, is the difficulty in achieving satisfactorily high R.sub.o A products needed for photovoltaic operation.
Another prior art detector is extrinsic silicon. This includes silicon with shallow dopants which give rise to spectral responses extending beyond 12 .mu.m, for example, Si:Ga detects radiation out to about 18 .mu.m, Si:As to about 24 .mu.m, and Si:Sb to about 30 .mu.m. Extrinsic Si detectors operating at these longer wavelengths require cooling well below 77.degree. K. Operating temperatures of these photoconductive detectors are below 20.degree. K. requiring liquid He as the cryogenic medium.
In the present invention there is disclosed a photon detector that can have a spectral response extending at least to about 100 .mu.m operates at liquid nitrogen temperatures (77.degree. K.) or higher. The present invention utilizes the photoeffects in high transition temperature superconductors such as YBa.sub.2 Cu.sub.3 O.sub.7 and utilizing as the principle of operation photon-assisted tunneling.